High voltage circuit interrupter with graded insulating operating rods



I w l li 5 win April 21; 1970- v. CHABALA HIGH VOLTAGE CIRCUIT INTERRUPTER WITH GRADED Filed Nov. 9. 1967 INSULATING OPERATING RODS 5 Sheets-Sheet 1 April 21, 1970 1.. v. CHABALA HIGH VOLTAGE CIRCUIT INTERRUPTER WITH GRADE INSULATING OPERATING RODS Filed Nov. 9, 1967 3 Sheets-Sheet 2 April 21, 1970 L. v. CHABALA 3,5 2

HIGH VOLTAGE CIRCUIT INTERRUPTER WITH GRADED INSULATING OPERATING RODS 5 Sheets-Sheet 5 Filed Nov. 9, 1967 QN\\ Nm QM, 9w 5% F k, f Q I I I [K .w in E M: W m f w E:

l .w.w I: kl m m @w I 9% mm: wiwr sbf I I F Q r J ii 1 @L N. m mm ww s f M m. a 3 3 as g 5% United States Patent 3,508,022 HIGH VOLTAGE CIRCUIT INTERRUPTER WITH GRADED INSULATING OPERATING RODS Leonard V. Chabala, Maywood, Ill., assignor to S & C Electric Company, Chicago, Ill., a corporation of Delaware Filed Nov. 9, 1967, Ser. No. 681,780 Int. Cl. H01h 9/38 U.S. Cl. 200-146 8 Claims 4 ABSTRACT OF THE DISCLOSURE The metal to insulation connections to the main and auxiliary operating rods for series connected main and auxiliary contacts are graded to inhibit voltage breakdown at these connections.

This invention is an improvement over the. invention disclosed in Mikos et al. US. Patent No. 3,163,736, issued Dec. 29, 1964.

In the circuit interrupter construction disclosed in the above patent a plurality of sets of series connected contacts are connected in parallel with the same number of sets of series connected auxiliary contacts. Provision is made for first opening the main contacts to transfer the current flow to the auxiliary contacts which are then opened to effect final circuit interruption. The sets of main and auxiliary contacts are interconnected by nonconducting tension-compression members in the form of insulating rods for the purpose of moving the main contacts between closed and open positions and moving the auxiliary contacts in like manner. The sets of main and auxiliary contacts are arranged in tandem and are operated from one end of each assembly. Large voltage increments exist between the moving contact sets when a high voltage circuit is interrupted. The voltage may be several thousands of volts. For example it may be 230 kv.

.The voltage that exists across a particular open contact set is bridged by the insulating rod or rods required to move the contacts located more distant from the operating ends of the tandem contact assemblies. Difiiculty has been encountered because the insulating operating rods failed due to shock loads incident to shipping of the interrupters from the factory to the site of installation and due to actual operation. In addition, failure of the insulating qualities of the rods has resulted from arcing over them.

After prolonged study and observation it was realized that certain factors were present which tended to cause these difficulties. The voltage gradient along the surface of the insulating rods was not uniform because the electric field around the terminals of these rods was not uniform. Since the insulating rods were joined to members which differed substantially from large sphere shapes, there was a great increase in dielectric stress that was augmented by the sharp edges of the openings where the insulating rods entered the contacts and rod ferrules. Electric field refraction occurred due to the difference between the dielectric constants of the insulating rods and the surrounding gas filled space.

Among the objects of this invention are: In a seriesp-arallel multigap high voltage circuit interrupter to reduce the likelihood of voltage breakdown between the insulaitng rods employed for operating the contacts and metallic connections thereto, to reduce are tracking and to reduce corona at these locations during the following interruption of the high voltage circuit; to contour the metal parts at the insulating rod connections for these purposes; at the connection between each main contact and its main insulating operating rod to countersink the main contact and receive one end of the insulating rod within the recess thus provided; to provide an insulating guide bushing at the recessed connection to the main con tact with one end of the guide bushing filling the space in the recess between the main insulating rod and the main contact and the other end of the guide bushing being spaced from the main insulating rod to assist in grading the voltage stress at this juncture; at the junction between a pull or auxiliary insulating rod and a movable auxiliary contact to provide a metallic shield over this juncture to prevent formation of corona and establish a relatively uniform voltage gradient; and to support each pull or auxiliary rod intermediate its ends by insulating bushings carried by metallic support plates and to reduce the voltage gradient at these locaitons by curving the edges of the metallic support plates at the ends of these insulating bushings.

According to this invention a series-parallel multigap high voltage circuit has electrostatically graded mechanical connections between the main and auxiliary contacts and the insulating rods which interconnect them for conjoint operation. Each main contact has a recess at one end for receiving its main operating insulating rod therein with an insulating guide bushing having one part filling the space in the recess between the main contact and its operating rod and another part spaced from this operating rod. A metallic shield overlies one of the connections between a pull or auxiliary insulating rod and its auxiliary contact to prevent formation of corona and establish a relatively uniform voltage gradient at these locations. The pull or auxiliary insulating rods are supported intermediate their ends by insulating bushings carried by metallic support plates the outer edges of which are curved to reduce gradually the voltage gradient between them and the insulating rods. By the introduction of insulation having a dielectric constant intermediate the dielectric constants of the surrounding insulating gas and the insulating operating rods, the voltage gradient therebetween is rendered more uniform.

In the drawings: FIGS. 1A-1B in end-to-end relation show a vertical cross sectional view of a circuit interrupter embodying this invention, the contact-s being shown in their closed positions. FIGS. 2A-2B placed end-to-end show a top plan view of the cont-act assembly within the insulating housing of the circuit interrupter shown in FIGS. lA-lB. FIG. 3, Sheet 1, is a vertical sectional view showing certain details of construction of the movable main contacts and the main insulating rods interconnecting them together with the voltage grading means therefor. FIG. 4, Sheet 2, is a vertical sectional view of one of the main insulating rod assemblies. FIGS. 5, 6 and 7, Sheet 3, are sectional and elevational views showing details of construction of the auxiliary insulating rods which are employed for interconnecting the movable auxiliary contacts to effect conjoint operation thereof.

In FIGS. 1A-1B and 2A-2B the reference character 10 designates, generally, a circuit interrupter of the kind and character described in the patent above referred to. The circuit intrrupter 10 includes an insulating housing 11 that is formed of porcelain or like insulating material which has termnals 12 and 13 hermetically sealed to the ends thereof and providing therewith a cylindrical space 14 that is filled with an arc extinguishing gas such as sulfurhexafiuoride. In addition there is located in the space 14 within the insulating housing 11 a seriespa'rallel multigap main and auxiliary contact assembly that is indicated, generally, at 15. The "assembly 15 is supported within the insulating housing 11 by the terminals 12 and 13 and by intermediate metallic support v plates 16. These supports also provide parallel internected in series circuit relation. Each set of main contacts 19 includes a pair of stationary main contacts 20 and 21 which are arranged to be interconnected by a movable main contact 22. The same number of auxiliary contacts, shown generally at 25, is employed that comprises the main contacts 19 and they are connected in parallel in the manner indicated. Three sets of tandem arranged auxiliary contacts 25 are shown in FIGS. 2A-2B. Each set of auxiliary contacts 25, FIG. 1A, includes a relatively stationary auxiliary contact 26 and a relatively movable auxiliary contact 27. The

arrangement is such that the main contacts 19 are openedfirst and the current'flow is transferred to the series connected auxiliary contacts 25 which then are opened and arcs are drawn between the respective stationary and movable auxiliary contacts 26 and 27. In order to assist in extinguishing these arcs, the arc extinguishing gas is directed by an insulating nozzle 28 to flow into the respective arc space as the result of pressure developed by pumps 29, one individual to each nozzle 28 as the auxiliary contacts 27 are moved away from the stationary auxiliary contacts 26. 'Extending laterally from opposite sides of the supports for the nozzles 28, as shown in FIGS. 2A-2B, are metallic arms 30 which are arranged to be interconnected in a manner to be described.

Voltage distributing resistors 31 are connected in parallel with the parallel connected main and auxiliary contacts 19 and 25. Each of the resistors 31 has a relatively high ohmic value so that the current flow therethrough is minimized when the main and auxiliary contacts 19 and 25 are opened. The resistors 31 are mounted on and connected to adjacent pairs of metallic support plates 16 as shown in FIGS. 2A-2B.

At the right end of FIG. 1B main and auxiliary contact operators 34 and 35 are shown. In the manner described in the patent above referred to provision is made for sequentially moving these operators 34 and 35 for first opening the main contacts 19 and subsequently for opening the auxiliary contacts 25 to eifect circuit interruption. The construction of the circuit interrupter thus far described is essentially the same as set forth the above patent.

When a high voltage circuit is opened, certain voltage stresses incident to the circuit opening operation are set up. In addition, after the circuit interruption has been completed, there are certain electrostatic stress distributions which may cause difiiculty by way of providing a restrike of the are that initially was interrupted. It is to the solution of problems incident to these conditions as above outlined that the present invention is addressed.

In FIGS. 3 and 4 the details of construction of the mechanical connections to the movable main contacts 22 are illustrated. For interconnecting the main insulating rods 36 are employed which are formed of fiber glass polyester which has a dielectric constant of about 5. Metallic ferrules 37 are provided at the ends of certain of the insulating rods 36. The metallic ferrules 37 are employed for the ends of the insulating rod 36 shown to the left of FIG. 3 and for the left end of the intermediate insulating rod 36 and illustrated in further detail in FIG. 4. The metallic ferrules 37 are suitably deformed by magnetic forming means as indicated at 38 into grooves that are provided in the respective end of the main insulating rod 36. Transverse retaining pins 39 extend from the movable main contacts 22 through the ferrules 37 and those portions of the insulating rod 36 therein to securely hold the parts in assembled relation. For the movable main contact 22 shown to the right of FIG. 3 and in FIG. 4. a ferrule 40 is employed which is somewhat longer than the ferrule 37 at the other end. As indicated in FIG. 4 it is magnetically deformed at 41 into suitable grooves formed in the underlying end of the rod 36. A locking bar 42 is located at the right end of the ferrule 40 and extends into the forward end of the main contact operator 34 to prevent relative rotation. The ferrules 37 and 40 are formed of suitable metal such as aluminum tubing while the locking bar 42 is formed of stainless steel.

In order to provide the proper voltage gradient between the left ends of the movable main contacts 22 and the main insulating rods 36 these ends are countersunk as indicated at 43 in order to receive the adjacent end of the respective main insulating rod 36. The countersunk end 43 provides a conical space which is filled by a frusto conical end 44 of a guide bushing 45 that preferably is formed in insulating material, such as polytetrafiuoroethylene, having a dielectric constant of about 2. As shown in FIG. 4 the other end 46 of the guide bushing 45 is rounded and an annular space 47 is provided between it and the juxtaposed surface of the main insulating rod 36.

At the left end of the left main movable contact 22, FIG. 3, an insulating guide 48 is provided of the same material as used for the guide bushings 45 and of a configuration such as to fill the countersunk end 43 in the manner previously described. A stem 49 extends from the insulating guide 48 and is held in place by the transverse retaining pin 39. The guide bushings 45 and the insulating guide 48 also perform a guiding function in directing the respective movable main contact 22 into contact engagement with the respective stationary main contact 20 when the assembly is moved to the circuit closed position.

FIGS. 5, 6 and 7 show in greater detail the manner in which the laterally extending metallic arms 30 from the supports for the nozzle 28 and relatively movable auxiliary contact 27 are mechanically interconnected and electrostatically graded. The mechanical connections are provided by two pairs of auxiliary insulating rods 51 that are formed of fiber glass polyester. Ends 52 and 53, FIGS. 5 and 6, are reduced in diameter for receiving ferrules 54 and 55 which are magnetically deformed thereon as indicated at 56 and 57. The ferrule 55 has an intermediate shoulder against which reacts one side of a radial flange 59 which forms an integral part of a metallic shield 60 which overlies the junction 61 be tween the left end 62 of the ferrule 55 and the insulating rod 51. The ferrules 54 and 55 and the metallic shield 60 preferably are formed of aluminum. The shoulder 58 provides reinforcing for the joint with the insulating rod 51, the joint being formed by magnetically inducing high current flow in the ferrules 54 and 55. The metallic shield 60 is spaced as indicated at 60' from the underlying surface of the insulating rod 51 and it has an annular bulbous section 63 for more uniformly distributing electrostatic stress at the junction with the respective insulating rod 51.

The ferrule 55 has an intermediate section 64 which extends through the respective laterally extending arm 30 on opposite sides of which cup washers 65 of aluminum are located for retaining 0 rings 66 of rubber like material. The extreme right end of the ferrule 55 is threaded as indicated at 67 for receiving a clamp nut 68 to secure the assembly to the respective arm 30 and properly position the metallic shield 60.

The ferrule 54 at the left end of each of the insulating rods 51 is interally threaded as indicated at 71 for receiving the threaded end 67 of the next ferrule 55. The ferrule 54 has an enlarged end section 72 for electrostatically grading the cup washers 65 and the adjacent end of arm 30. The ferrule 54 tapers gradually as indicated at 73 to a smaller diameter. The intermediate laterally extending metallic arm 30 is clamped as indicated in FIG. 5 between ferrules 54 and 55 in a manner that will be apparent.

At the left end of FIG. 5 it will be observed that a metallic bolt 74 extends through the laterally extending arm 30 at this location andis threaded into the thread 71 of the ferrule 54. The bolt 74 is employed for clamping the assembly on the arm 30.

As .shown in FIGS. 2A2B and in FIGS. 5 each of the auxiliary insulating rods 51is guided through a pair of adjacent metallic support plates 16. To reduce friction, guide bushings 75 and 76 are employed. They are formed of suitable insulating material suchv as polytetrafluoroethylene having a dielectric constant" of about 2. Since the metallic support plates 16 are momentarily at different potentials from that of the insulating rods 51, the edges of the metallic support plates 16 are convexly rounded as indicated at 77 to provide a gradual transition of the voltage gradient between them and the insulating rods 51 and a more uniform electrostatic stress distribution.

By employing the voltage grading and electrostatic stress distribution constructions for the mechanical connections to the main insulating rods 36 and to the auxiliary insulating rods 51, the likelihood of voltage breakdown at these locations and the creation of corona during and after circuit interruption are greatly minimized. The insulating rods 36 interconnecting the main movable contacts 22 have the guide bushings 45 at the junction with the left ends of these contacts which are progressive- 1y more distant from the main contact operator 34. Since the dielectric gas, SP has a dielectric constant of about 1, the guide bushings 45, which have a dielectric constant of about 2, provide a more uniform voltage gradient from the insulating rods 36 which have a dielectric constant of about 5. This relieves electric flux concentration as do the conical surfaces of the countersunk ends 43 of the main contacts 22 which provide smooth edged cavities for receiving the adjacent ends of the insulating rods 36. A similar effect is provided by the annular spaces 47 where the insulating rods 36 enter the guide bushings 45. At the right ends of the auxiliary insulating rods 51, where the voltage gradient heretofore has caused difliculty, the bulbous sections 63 of thejmetallic shields 60 produce a more uniform electric field since they provide surfaces approaching sphere-like surfaces. The rounded edges of the bulbous sections 63 where the ends of the insulating rods 51 enter the spaces 60' and the depths of these spaces reduce localized electric field distortion and spread the electric field along substantial lengths of the auxiliary insulating rods 51. This is of great importance sincethe electric flux density in the rods 51 is about five times the electric flux density in the surrounding SP The voltage gradient between the auxiliary insulating rods 51 and the metallic support plates 16 is made more uniform and local electric field distortion is minimized by the convexly rounded edges 77 of the support plates 16 and by the guide bushings 75 and 76 which have dielectric constants of about 2. This is intermediate the dielectric constants of the surrounding SP and of the auxiliary insulating rods 51.

In order to insure smooth and clean surfaces for the main insulating rods 36 and auxiliary insulating rods 51 they are coated with a suitable varnish. This reduces the likelihood of the development of local voltage stresses which high dielectric strength glass hairs might develop. As a result it has been possible to utilize the circuit interrupter for severe circuit interrupting purposes.

The use of fiber glass polyester for the main insulating rods 36 and the auxiliary insulating rods 51 has overcome the breakage problem to which prior insulating rods were subject. Because of the high strength and lack of brittleness of fiber glass polyester, these insulating rods are practically unbreakable and are capable of withstanding mechanical shock incident to shipping and operation. By grading the ends of the insulating rods of glass polyester in the manner herein disclosed, it has been possible to neutralize the differences in dielectric constants of the different insulating materials involved and thus to minimize the generation of corona and incidental arcingand tracking.

What is claimed as new is:

1. In a high voltage alternating current circuit interrupter:

an elongated insulating housing having terminals sealed to its ends and providing therewith a pressure tight closure,

a pair of parallel connected sets of series connected separable main and auxiliary contacts in said housing interconnecting said terminals, each set including relatively stationary main and auxiliary contacts and 'relatively movable main and auxiliary contacts-for engaging and disengaging the respective relatively stationary main and auxiliary contacts,

a main insulating rod mechanically interconnecting said movable main contacts,

means for electrostatically grading the mechanical connection between one of said main contacts and said main insulating rod,

at least one auxiliary insulating rod mechanically iiiterconnecting said movable auxiliary contacts,

means for electrostatically grading the mechanical connection between one of said auxiliary contacts and said auxiliary insulating rod,

an arc extinguishing gas within said housing at a pressure above atmospheric pressure,

said one main contact having a central endwise extending opening therein enlarged at one end and said main insulating rod extending from said one end, and

an insulating bushing telescoped over said main insulating rod and at one end extending into the enlarged end of said opening in said main contact and at the other end being internally spaced from said main insulating rod.

2. The circuit interrupter according'to claim 1 where in said main insulating rod has a dielectric constant higher than the dielectric constant of said insulating bushing.

3. The circuit interrupter according to claim 2 wherein the dielectric constant of said main insulating rod is about 5, the dielectric constant of said insulating bushing is about 2, and the dielectric constant of said gas is about 1.

4. In a high voltage alternating current circuit interrupter:

an elongated insulating housing having terminals sealed to its ends and providing therewith a pressure tight closure,

a pair of parallel connected sets of series connected separable main and auxiliary contacts in said housing interconnecting said terminals, each set including relatively stationary main and auxiliary contacts and relatively movable main and auxiliary contacts for engaging and disengaging the respective relatively stationary main and auxiliary contacts,

a main insulating rod mechanically interconnecting said movablemain contacts,

means for electrostatically grading the mechanical connection between one of said main contacts and said main insulating rod,

at least one auxiliary insulating rod mechanically interconnecting said movable auxiliary contacts,

means for electrostatically grading the mechanical connection between one of said auxiliary contacts and said auxiliary insulating rod,

an arc extinguishing gas within said housing at a pressure above atmospheric pressure,

at least one metallic arm extending laterally from each movable auxiliary contact and said auxiliary insulating rod mechanically interconnecting said arms,

a metallic ferrule telescoped over said auxiliary insulating rod and connecting it to the arm of said one auxiliary contact, and

a metallic shield connected to said metallic ferrule and overlying the juncture between said auxiliary insulating rod and said ferrule.

5. The circuit interrupter according to claim 4 wherein said metallic shield has a bulbous distal end and is spaced for a substantial portion of its length from the surface of said auxiliary insulating rod;

6. The circuit interrupter according to claim 4 wherein said auxiliary insulating rod is supported intermediate its ends by at least one metallic support plate,

an insulating bushing is interposed between said metallic support plates and said auxiliary insulating rod, and

those edges of said metallic support plate adjacent said insulating bushing are convexly rounded.

7. The circuit interrupter according to claim 6 wherein said auxiliary insulating rod has a higher dielectric constant than said insulating bushing.

References Cited UNITED STATES PATENTS 2,835,725 5/1958 Nicholas 174144XR 3,163,736 12/1964 Mikos et al. 200-146 HERMAN O. JONES, Primary Examiner US. Cl. X.R. 7 174144 

